Reorganisation of mine dewatering operations
The 13 water pumping stations managed by RAG Aktiengesellschaft, Essen/Germany, that were operating in the Ruhr coalfield in 2018 are now to be reduced in number to the required minimum of six stations (Figure 1) and these will each be assigned to functionally separate water management zones.
Fig. 1. Location of mine water pumping stations in the Ruhr area according to the new management plan. // Bild 1. Wasserhaltungen im Ruhrgebiet nach Umsetzung des Konzepts. Source/Quelle: RAG
In the Ibbenbüren coalfield the mine water from the Westfeld workings, which closed in 1979, has since 1983 been able to flow under gravity to the surface via the Dickenberg adit. There are also plans to raise the mine water level in the Ostfeld workings to a target height of 63 m above sea level so that the mine water in this area can also be channelled under gravity via a drainage adit that leads into the Hörstel Aa river (Figure 2).
Fig. 2. Planned mine water drainage measures for the Ibbenbüren coalfield. // Bild 2. Wasserhaltung im Ibbenbürener Revier nach Umsetzung des Konzepts. Source/Quelle: RAG
Protection aims enshrined in the mine water drainage plan
A complete shut-down of mine water pumping operations after the cessation of coal winning will present a number of safety concerns. Given the existence various influencing factors, as depicted schematically in Figure 3, the following protection objectives will have to be borne in mind when implementing the mine water management plan:
- The stability of any backfilled and disused shafts must not be compromised, otherwise there could be a risk of sinkholes developing.
- The rise in mine water level must not result in the uncontrolled escape of mine gas to the surface.
- The rise in mine water level, and the associated ground movements, must not produce any damaging impact at ground level within the meaning of § 55 (1) no. 9 of the Federal Mining Act (BBergG): Significant impairment of property at ground level as defined in the judgment of the Federal Administrative Court of 16th March 1989 (4 C 36.85), or cause damage that might impair the functioning of municipal facilities (Decision of the Higher Administrative Court of North Rhine-Westphalia of 5th September 2003 (21 B 2517/02)) (Minimising the risk of serious subsidence damage).
- The mine water level must not be allowed to rise to such a degree that the near-surface groundwater horizons requiring protection are not adversely affected by the input of highly saline deep groundwater (risk of a threat to drinking water and service water supplies).
Fig. 3. Schematic overview of individual factors likely to impact on mining operations. // Bild 3. Schematische Darstellung der einzelnen Wirkfaktoren für den Bergbau. Source/Quelle: Bezirksregierung Arnsberg
The mining authorities of North Rhine-Westphalia take these protection aims into account by ensuring that all salvage, dismantling and safety work being undertaken as part of a mine closure operation undergoes intensive scrutiny as part of the obligatory approval procedure. The work in question forms part of the Final Operational Planning Procedure (ABP) regulating the orderly withdrawal from the underground workings. This incorporates a monitoring concept that includes the implementation phase of the ABP and the process for managing the rise in mine water level after ABP implementation.
Monitoring programme
A regional monitoring programme is now to be introduced throughout the Ruhr coalfield area. This cross-location observation system is designed to establish whether the predictions made in the approval process are actually becoming a reality. This includes the development of mine water levels and mine water quality and the impact of this at ground level, and in particular the avoidance of critical gas emissions and ground movements. The knowledge gained will also enable controlling measures to be put in place if developments give indications of detrimental deviations from the set targets. A similar monitoring programme is also planned for the Ibbenbüren coalfield.
Water management aspects of the rise in mine water levels
Increasing depth tends to be accompanied by increasing levels of salts, especially chloride and sulphate, and of heavy metals in the mine water (deep groundwater). In certain cases, and when the barium salt content is at a certain level, measurable radioactive contamination may also be present. This radioactivity has its origin in natural hydrothermal activity as the deep groundwater that is discharged in the form of mine water from the underground workings carries these constituent elements with it as it makes its way up through the formations. Chloride and sulphate are substances that become dissolved as the water passes up through the strata. The formation of sulphates is promoted by the admission of air from the mine ventilation system. This admission of air leads to an oxidation of sulphide compounds, with the result that there is an alteration of the sulphides, which are transformed into water-soluble sulphates, and of the metals found in the ore minerals, such as iron.
The increase in mine water to the proposed target level can inhibit the aforementioned processes in and around the flooded mine workings. The initial elution phase is followed by a long-term reduction in the amount of sulphate-based metal compounds being flushed out with the mine water. Moreover, pumping the mine water out from shallower depths means that the overall heavy-metal and salt content tends to be less than was previously the case. This fact, in conjunction with the adjustment of the volume of water being transferred, means that the surface water bodies into which the mine water is pumped are significantly relieved of contamination.
The ABP process also includes the use of a well-established evaluation procedure to predict the kind of changes that may be expected in the quantity and contaminant load of the mine water that will be pumped out of the workings in the years ahead. If these findings indicate that the anticipated effects (see above) alone are not sufficient to achieve a mine water quality in the long term that is compatible with the aims of establishing a good chemical and environmental status in the receiving surface waters the approval process also contains the proviso that the mine water being extracted from the workings must be cleaned in a suitable water treatment plant.
In addition to these natural contaminants mine water can also be affected by various anthropogenic pollutants:
Following a serious underground fire at a Belgian colliery the coal industry began to use PCBs, and the later substitute TCBTs, in order to increase the fire protection properties of hydraulic fluid. This practice continued from 1964 to the beginning of the 1980s. Subsequent identification of the environmental toxicity of these substances resulted in them being banned from use. However, the escape of hydraulic oil from plant and machinery over the years has meant that these substances are still to be found at individual locations below ground and may also have been transferred accidentally around the mine workings, thereby creating various diffuse pollution points. The toxic material is discharged as trace contaminants with the mine water as it is pumped to the surface.
In this context the Federal State Government commissioned a report whose findings concluded, among other things, that a rise in mine water level would have a fundamentally positive impact in terms of minimising the discharge of PCBs due to mine water pumping operations. The implementation of the Mine Water Management Plan therefore also serves the purpose of reducing to a minimum the material pollution of water bodies due to the input of PCBs (1). The salvage and dismantling work to be undertaken below ground first has to undergo an expert appraisal so that by deploying measures based on this analysis any PCB contamination below ground can be kept to a minimum as the salvage operation is carried out and, as a result, the recommendations contained in the aforementioned report can be implemented as part of the Final Operational Plan.
A special sampling campaign organised by the North Rhine-Westphalian State Agency for Nature, Environment and Consumer Protection (LANUV NRW) also established that the PCB content of the mine water did not conflict with the pertinent environmental quality standards at any of the examined measuring points in the relevant water bodies. An experimental facility has also been set up above ground to investigate whether the PCB content can feasibly be further reduced by treating the mine water after it has been pumped to the surface.
As well as PCB pollution there is also the question of whether the use of non-mining waste material for underground stowing operations could have resulted in some form of contamination of the mine water, especially due to an input of heavy metals, as mine water levels rise.
The use of non-mining waste as stowing material in the coal mines of North Rhine-Westphalia was mainly a feature of the period 1985 to 2006. During this time the practice of filling underground cavities was regarded as a way of recycling large quantities of industrial waste. Waste material with a low pollutant potential was deployed in this way according to the principle of “immission neutrality”. Material with a higher pollutant potential was used by applying the principle of “complete containment”. These operating principles, which classified non-mining waste on the basis of its hazard potential, were defined in a feasibility study that was carried out on behalf of the former State Water and Waste Authority (LWA). By observing certain boundary conditions it was possible to establish that the required barriers were in place and that evidence was provided of long-term stability over the period following the closure of the mines, to the effect that there was no risk of any adverse change in the quality of the groundwater within the meaning of § 48 (1) of the German Water Resources Act (WHG).
The first part of the State Government report on the filling of underground voids and cavities seeks to examine the assumptions and findings of the LWA study and the manner of its application, with a focus on Haus Aden colliery. This expert review concluded that there were no reasons to be concerned about any risk to surface water bodies or to groundwater supplies. The mine water analyses that have been conducted on a regular basis over the last ten years were confirmed as fully sufficient for the monitoring process. This conclusion was reaffirmed in the more detailed analysis presented in the second part of the report.
Legal implementation and public consultation
An operational planning permit is required not just for ongoing mining operations but also when a colliery is being prepared for closure. In this case the authorisation is provided by way of a Final Operational Planning Procedure (ABP). The implementation of the mine water management plan therefore involves several ABP stages that may include the following individual steps, depending on the local situation:
- withdrawal from the last remaining section of mine workings;
- conversion of the existing central pumping system to well-type operation;
- permanent abandonment of those pumping stations that are no longer required.
One of the stages in the ABP process involves an investigation of the effect of rising mine water levels. This includes the impact on mine shafts and surface openings where the backfill does not meet long-term stability requirements. This process also requires clarification, in accordance with § 48 (2) BBergG, as to whether the water body-compatible infeed of mine water is generally possible given the quantity and quality arising after the target level has been reached, and taking account of the reduced discharge of PCBs. Water law permits are also required, in addition to ABP approvals, for the remaining water pumping stations. A definition of the themes to be examined in these procedures is given in Table 1.
Table 1. Thematic breakdown of the Final Operational Planning Process and Water Law Authorisation Process. // Tabelle 1. Thematische Aufgliederung des Abschlussbetriebsplan- und des wasserrechtlichen Erlaubnisverfahrens. Source/Quelle: Bezirksregierung Arnsberg
The issuing of licences for any future central mine dewatering stations gives authorisation for mine water to be pumped to ground level and fed into the surface water bodies, after treatment if necessary. For a water law permit to be granted either a full Environmental Impact Assessment (EIA) must be carried out or, depending on the volume of mine water being extracted, a preliminary review has to be undertaken of the need for an EIA, this to be followed if appropriate by the EIA process itself. The legal basis for this is laid down in the Environmental Impact Assessment Act (UVPG). The latter contains rules relating to the participation of other authorities and of the public too.
The ABP process for the abandonment of the mine workings and the conversion of water pumping stations to well-type operation does not usually provide in law for any public involvement. This would only be the case if the application dossier raised certain fears about the impact of the operation on surface structures, e. g. significant damage to buildings as defined in the Moers-Kapellen ruling. However, the RAG Mine Water Management Plan and the associated commitment to a target mine water level, along with the requirements imposed by the mining authorities for the granting of ABP permits, are such that any impact of this kind is not expected. In any case, RAG has been called upon by the Mining Authority in North Rhine-Westphalia to keep the public suitably informed on any forthcoming projects by way of an information and communication strategy and to set up a platform where suggestions and objections can be voiced.
Safeguarding drinking water supplies is an issue of overriding public interest and also constitutes a mandatory certification requirement within the ABP process. In addition, bodies responsible for public water supply are included in the water law process by the Mining Authority through the various associations and organisations, as the parties concerned, in the same way as public interest bodies. Moreover, both the Mining Authority of North Rhine-Westphalia and the RAG company each maintain their own dialogue with these associations with a view to addressing and allaying any concerns that may arise. This ensures that the interests of all citizens are properly protected as far as the supply of safe drinking water is concerned.
Depending on the volume of water to be pumped annually the water law permit process requires an EIA review or an obligatory EIA process. In the case of an EIA review the results of this preliminary assessment are published in the official journal of the administrative district concerned and also in the official journal of the Arnsberg District Government, the latter being an abiding requirement due to the jurisdiction exercised by the Mining Authority of North Rhine-Westphalia. If the preliminary review indicates that an EIA is needed because of the significance of any potential adverse environmental effects the procedure adopted is that of a general EIA. In this case the application dossier is the subject of a public notice and the documents are opened to public inspection. A deadline is then set for the lodging of objections by those who may be affected by the works. These objections will at a later date be the subject of a public hearing that is also subject to public disclosure. The subsequent ruling is announced locally in accordance with legal requirements and is then published in the official journal of the administrative district concerned, as well as in the official journal of the Arnsberg District Government and in the Federal Government’s EIA portal. As regards the raising of objections it should be noted that the final decision will only consider those protests whose content relates to the themes covered by the water law process (Table 1) and that are relevant to the period under consideration, as defined for the purposes of the EIA.
State of proceedings and future outlook
During the period when salvage and dismantling work is under way below ground water law permits will be issued for those water pumping stations that are currently in operation and will also be required for the foreseeable future. These operating permits will relate to the operating status of the stations to date. Extensions to these operating permits will be required for a transitional period to cover the stations at Friedlicher Nachbar, Heinrich and Robert Müser (Ruhr catchment area) and at Amalie, Concordia and Zollverein (Emscher catchment area).
In the course of the ABP process for the implementation of the mine dewatering plan for the eastern part of the Ruhr region an ABP extension was granted on 7th December 2017 for the central drainage operations being carried out below ground at Haus Aden. This operating permit covered the withdrawal from the remaining mine workings and the implementation of measures aimed at minimising any degradation caused to the underground workings due to the uptake of PCBs and the cessation of water pumping operations below ground, with the resulting rise in mine water level to 600 m below sea level. This work was completed in September 2019. The site in question was the subject of a water law permit process with EIA.
Another step was taken towards implementing the mine water management plan for the central Ruhr region with the approval of the ABP for the central pumping station at Auguste Victoria in September 2018. This operating permit covers the work needed to arrange for the final withdrawal from the remaining section of mine workings and to ensure a rise in mine water level to 600 m below sea level. Setting the increase at this level will ensure that the natural drinking water reserves of the Haltern sands will not be compromised in any way, this being guaranteed by maintaining a safe distance to the drinking water horizon in that area. In order to safeguard this mine water level the Auguste Victoria site is to be converted to serve as a back-up site. The operation of raising the mine water and feeding it into the Lippe river at this point in the event that back-up capacity is needed has now been established as licensable in a feasibility study.
The ABP for Prosper-Haniel colliery in Bottrop, the last active coal mine in the Ruhr coalfield, was submitted to the Mining Authority in the final quarter of 2019. This also involved a partial withdrawal from the mine workings under the provisions of the current Master Operating Plan. The outcome of the ABP application for Prosper-Haniel will depend to a large degree on the findings of the feasibility study undertaken at the Lohberg site (see below). This study will seek to establish that the implementation of the ABP at Prosper-Haniel, along with further ABPs at other sites in the central Ruhr area, will not create the conditions that would prevent approval being granted on water management and water legislation grounds.
This step is needed because the timetable for the completion of the upcoming water law processes resulting from the mine water management plan, which have to be carried out successively, will run for a period of about six years commencing in 2019, but the permits for the aforementioned ABPs are required in advance in order to be able to execute the withdrawal work that is needed partly for mine safety reasons and to arrange for the conversion to well-type water extraction in the drainage area of the future Lohberg mine water management zone.
The next proposed step is to carry out the ABP procedures required for the water pumping sites of the central Ruhr area – the so-called Emscher line – comprising the Zollverein, Amalie, Concordia and Carolinenglück stations. This will all be part of the ongoing implementation of the Mine Water Management Plan. The aim of the ABP procedures at the Zollverein, Amalie, Carolinen-glück and Concordia sites is to facilitate a withdrawal from the remaining mine workings and to arrange for mine water levels to rise to some 600 m below sea level.
For the currently inactive installation at Lohberg, with its Lohberg and Hünxe pumping stations, the plan is to withdraw from the remaining mine workings and to convert to a well-type system between 2022 and 2024. The ABPs that are required for this project, which will authorise long-term operations, are to be approved in due time by the Mining Authority. The mine water produced from the Auguste Victoria and Prosper-Haniel sites and from the central Ruhr area will in future be channelled below ground to Lohberg and all these inflows will be combined and pumped to the surface before being fed into the Rhine. This operation requires a water law approval procedure with EIA, which is expected to commence at the end of 2020.
The more southerly sites in the Ruhr catchment zone, namely the Robert Müser, Friedlicher Nachbar and Heinrich pumping stations, are also to be converted to a well-type system as part of the ABP process. The operation to raise the mine water level has mainly been concluded in this area. One of the final measures still to be taken is at Heinrich central pumping plant where the mine water level is to be raised from 480 m to 200 m below sea level. This process also requires a water law approval procedure with EIA, whereby the three sites in the Ruhr catchment area are to be combined as part of a cumulative operation.
In the western part of the Ruhr coalfield the mine water management plan, with its ABP permits for underground operations at the former Walsum and West collieries, has already been completed. The central pumping plant at Walsum was converted to well-type operation between 2011 to 2014. After the specified pumping level of 746 m below sea level was reached on 2nd June 2016 the well system was able to go into regular operation. After the former West colliery ceased pumping mine water in 2013 water levels have continued to rise in this zone of operation. The mine water produced on the left bank of the Rhine is expected to be transferred to the central pumping facility at Walsum in 2020. The well-based system is to be managed under the current Master Operating Plan. The ABP that regulates the long-term operation of this site was approved by the Mining Authority in 2019. The procedure whereby the water law permit is amended because of the impending admission of mine water from the former West colliery workings, which includes an EIA review, is expected to be completed in early 2020.
The ABP for Ibbenbüren colliery was submitted to the Mining Authority at the end of the first quarter of 2019. A partial withdrawal from the workings, without any change in the current mine water level, has been under way since the end of 2018 as part of the ongoing Master Operating Plan. The ultimate abandonment of the mine workings, which will result in the mine water rising to the planned level of 63 m above sea level, can only take place once the final closure plan – which has already been submitted – has been approved. The water infeed parameters for the Ibbenbüren site are still being clarified, which is why an EIA review, and possibly a full EIA too, will be necessary for this location.
Following the successful implementation of the Mine Water Management Plan the central pumping stations in the Ruhr coalfield will be reduced from 13 to six permanent installations, and those in the Ibbenbüren coalfield from four to two. This will relieve some 240 km of watercourses in North Rhine-Westphalia from an infeed of mine water. The Emscher river will then be completely free of mine water discharge.